Low temperature thermal conductivity of the noncentrosymmetric superconductor LaRhSi$_3$

We report results of low temperature thermalconductivity, $\kappa$, on single crystalline LaRhsi3. This compound crystallizes in tetragonal structure which lacks space- inversion symmetry. It is a moderate type II superconductor with a superconducting transition temperature of $T_c$=2.26 K, an upper critical field of only $H_{c2}=200$~Oe, and a first critical field $H_{c1}=120$~Oe. Immediately below $T_c$, the thermal conductivity has an exponential temperature dependence down to $T=0.4$~K. At low temperature $\kappa$ adopts a quadratic temperature dependence which changes suddenly to a cubic behavior only for fields around $H=H_{c1}$ and then becomes linear at higher fields. The magnetic field dependence of the residual linear term of thermal conductivity suggests an $s-$wave symmetry of the superconducting order parameter.